ABSTRACT Detecting change in neuropsychological functioning over time is critical for proper diagnosis and management of many neurological, psychiatric, and psychological conditions. It is well documented that most commonly used cognitive assessments produce significant retest effects, such as practice and regression-to- the-mean effects. Retest effects can cause substantial changes in test scores between assessments and make it virtually impossible to distinguish between true changes in cognitive performance and changes caused by repeated testing. Failure to account for such retest effects can lead to diagnostic disagreements, failure to detect deleterious effects of an illness or injury, or inappropriate attribution of improved scores to recovery or response to treatment. In this Phase I STTR application, we propose to develop and evaluate the Cognitive Change Battery (CCB), a, non-verbal, tablet-based cognitive assessment instrument for serial neuropsychological evaluations. The CCB adopts novel cognitive tasks that are resistant to practice effects and integrates them with a Bayesian regression model to correct for regression-to-the-mean and remaining practice effects. The complete test battery will measure four psychometrically distinct cognitive domains: (1) working memory, (2) long-term memory, (3) processing speed, and (4) executive inhibition. The resulting battery will provide clinicians with an instrument that (a) allows valid assessments of a patient?s initial neurocognitive status, delivered as a composite score reflecting general cognitive performance and subtest scores for the four distinct cognitive domains, (b) enables unambiguous interpretation of changes in neurocognitive status over time, and (c) is composed of cognitive tests that do not require language and are therefore suitable for non- English-speaking and language-impaired populations. Phase 1 of this project will determine the psychometric qualities of the CCB, including the absence of retest effects, in a sample of N=160 subjects. For Phase 2 of this project, we will develop additional tests, so that each cognitive domain will be represented by at least two subtests, and establish population norms for adults age 18 to 85 years.